If you're having problems booting the Solaris Express Community Release (necessary to Build OpenSolaris), try unplugging any USB devices you have connected to the system (especially if it's a Logitech Optical USB Mouse). There's a bug right now that prevents some systems with certain USB Mice from being able to properly boot the Solaris Express Community Release. I have been told that a fix will be put out for this soon.
Additionally, when you have any problems booting the Solaris Express Community Release, you should read Dan Mick's blog entry about debugging the boot process so that you can provide more information to those who can fix it.
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